V-belts and V-ribbed belts are used in a wide range of environments. V-ribbed belts are preferred for their high power transmission capability, which is attributable to the large contact area between the ribs on the belt and the flank on the cooperating pulleys.
In operation, there is a tendency for V-belts and V-ribbed belts to emit noise; a common complaint, especially on automotive drives. Belt noise is predominately the result of pulley engagement and disengagement noise arising as the ribs on the belt enter into and exit from the pulley grooves or arising from excessive rotational slip of the pulley relative to the belt. Rotational slip occurs during rapid acceleration or deceleration of the drive such as is encountered during shifting, engine startup or engine shutdown or due to excessive loading or insufficient wrapping around the pulleys.
It is preferable to have adequate and consistent traction between V-ribs on the belt and the pulley grooves in both wet and dry operating conditions. A common method of quantifying the traction level is by reference to the “effective coefficient of friction” (μe) as defined in SAE J2432, the entirety of which is incorporated by reference herein. Conventional V-ribbed belts have μe values ranging from about 0.4 to 2.1, but the preferred range for automotive accessory drives is about 0.7 to 1.5.
The effective coefficient of friction for existing V-rib belts generally varies drastically depending upon the environmental conditions at the time of use. In wet conditions, μe is at the lower end of the range due to the lubricating effect of water between the belt and pulley flanks, and in dry conditions μe is at the higher end of the range. Therefore, to achieve the goal of consistent traction in both dry and wet operating conditions, it is necessary to simultaneously lower the dry traction level while increasing the wet traction level.